Lighting systems are an integral part of the film, television, video, motion picture, and photography industries. Proper illumination is necessary when filming movies, television shows, or commercials, when shooting video clips, or when taking still photographs, whether such activities are carried out indoors or outdoors. A desired illumination effect may also be ordered for live performances on stage or in any other type of setting.
Various conventional techniques for lighting in the film and television industries, and various illustrations of lighting equipment, are described, for example, in Lighting for Television and Film by Gerald Millerson (3rd ed. 1991), hereby incorporated herein by reference in its entirety, including pages 96-131 and 295-349 thereof, and in Professional Lighting Handbook by Verne Carlson (2nd ed. 1991), also hereby incorporated herein by reference in its entirety, including pages 15-40 thereof.
Fresnel lenses were designed originally to allow for large geometry lensing in lighthouses, well before the advent of the true incandescent light bulb. Fresnel lenses were later used in early theatrical and movie lighting fixtures because they allowed the light to be shaped into beams of smooth light that could project for great distances. Such lighting fixtures are commonly referred to as “Fresnels.”
As stated above, Fresnel fixtures including glass lenses were and are used for film, television, motion picture, and live theatre applications. Typical Fresnel fixtures consist of a metal housing, reflector, light bulb assembly, and Fresnel lens. Fresnels fixtures for theatrical applications are commonly available in lens diameters of 3, 6 or 8 inches with globes ranging in power from 150 W (typically with a 3-inch Fresnel lens) to 2000 W (with an 8-inch Fresnel lens). In film, television, and motion picture lighting, a much greater range of lens and bulb sizes are typical. For these applications, lenses commonly range in size from 2 to 24 inches, and light bulb power ranges between 200 W and 20,000 W.
Known Fresnel fixtures may have a mechanism for changing the focal distance between the light bulb and the lens. Many Fresnel fixtures allow the light bulb inside the fixture to be moved relative to the lens focal point to increase or decrease the size of the projected light beam. Such adjustment, typically accomplished via a knob on the back of the fixture, varies from a narrowly focused beam (spot) to a wider beam (flood). Fresnel fixtures have been known to produce a beam as narrow as 7° or as wide as 70°.
Fresnel fixtures are useful in the film, motion picture and television industries not only because of their ability to focus a brighter beam than a typical lens, but also because the projected light is of relatively consistent intensity across the entire width of the beam. Fresnel fixtures are also known to produce a very soft-edged beam which makes them suitable for use as a wash light. In still photography, Fresnel fixtures have been used as a highlight, sidelight/backlight or kicker. A frame in front of the lens is often used to hold a gel to tint the light or wire screens to reduce it or frosted plastic to diffuse it. Barn doors are commonly used primarily to control light spillage or to shape the light.
However, this is not to say that existing (and historical) Fresnel lighting fixtures are efficient in any way. These conventional lighting fixtures have drawbacks or limitations which can limit their flexibility and/or effectiveness. Most of the light that is emitted by an omni-directional light bulb inside known Fresnel fixtures actually strikes and is absorbed and wasted by the cylinder shaped housing of these fixtures. A small portion of the light is bounced off a curved mirror in the back of the fixture and a small portion goes directly out the Fresnel lens. This leaves relatively little of the total light generated to be able to exit the Fresnel lens as harnessed light. Incandescent bulbs are very inefficient to start with and by then introducing them into a Fresnel housing their efficiency drops even further. Moreover, the reflector cannot be larger than the lens aperture, and thus all the radiated light that is neither redirected forward by the spherical reflector behind the bulb nor emitted directly through the lens is absorbed by the casing as waste heat. The major drawback of Fresnel fixtures is the enormous amount of heat energy generated by the bulbs and absorbed by the casing.
There are many existing Fresnel fixtures being used in the television and motion picture industries. These fixtures have inefficient incandescent bulbs but otherwise are solid and very well made. There is also an enormous amount of existing supporting infrastructure that is meant to power this old equipment such as the power grid and dimmer electronics and dimmer control boards which represent what was a large capital investment.
It would be huge commercial advantage if there were some way to simply and affordably upgrade these existing Fresnel fixtures to work with LED illumination sources that utilized as much of the existing supporting infrastructure as possible. There are multiple challenges to this approach in that there are enormous thermal challenges in matching the high flux densities in incandescent Fresnel fixtures using LED emitters not to mention simply discharging that heat. There are also several types of electrical power that existing power grids and dimmer electronics use, such as Triac based dimmers which use AC power and simply turn on the power at predetermined intervals in relation to the AC sine wave phase; Variac dimmers which use variable transformers, which vary the amplitude of the AC voltage; and though antiquated, even DC power systems which power lighting fixtures in an isolated manner so that they can be used around water and in other hazardous situations. None of these power systems are directly suitable to be used with LED based emitters.